Development of protective immunity to Litomosoides carinii will be explored by transferring lymphoid cells, serum or both to examine their ability to retard infections in syngeneic Meriones unguiculatus. Serum will be assessed for antibody using indirect hemagglutination and passive cutaneous anaphylaxis. Lymphoid cells will be assessed for sensitization by their responses to various mitogens and to specific antigens. The ability to retard infections will be judged by serial sacrifice of hosts to count and measure larvae or adults. Cell populations and immunoglobulins will be characterized using appropriate separation techniques and the same basic protocol. The rejection of transplanted L. carinii will be investigated by immunization of Mastomys natalensis with antigens made from 4th and 5th stage larvae. Adult worms will be transplanted into the peritoneal cavities of these immunized animals. The ability to transfer the capacity to reject transplanted worms with lymphoid cells will be assessed by the method described above. Cell populations will also be characterized. Interaction of the immune response and therapeutic drugs will be characterized by treatment of infected M. natalensis with diethyl-carbamazine followed by use of the mixed antiglobulin technique to assess acquisition of immunoglobulins and to complement components by microfilariae. Effects of the drug on the surface of the microfilariae will also be investigated. Immunopotentiation of DEC activity will be attempted by sensitizing infected M. natalensis with BCG, C. parvum, staphylococcal phage lysate or levamisole followed by the treatment with DEC. Potentiation will be judged by speed of microfilarial clearance. Animals will be sequentially sacrificed and liver sections examined for cleared microfilariae and associated cells. The protocol will be repeated using injected microfilariae to assess the effect of immunopotentiation on the microfilariae alone.